Chiral Terminal Platinum(II) Phosphido Complexes: Synthesis, Phosphorus Inversion, and Acrylonitrile Insertion

The chiral Pt(II) phosphido complex Pt(dppe)(Me)[P(Mes)(Men)] (dppe = Ph 2 PCH 2 CH 2 PPh 2, Mes = 2,4,6-Me 3 C 6 H 2, Men = (−)menthyl, 1 ) was prepared by proton transfer from racemic mesityl(−)menthylphosphine to the methoxide ligand of Pt(dppe)(Me)(OMe). Treatment of Pt(dcpe)[CH(Me)(CN)](Br) with alkali metal phosphides gives Pt(dcpe)[CH(Me)(CN)](PRR‘) (dcpe = Cy 2 PCH 2 CH 2 PCy 2, Cy = cyclo-C 6 H 11, R = H, R‘ = Mes* = 2,4,6-( t -Bu) 3 C 6 H 2, 13; R = Me, R‘ = Ph, 14 ). The related series of complexes Pt(diphos*)(Me)(PRR‘) (diphos* = S, S -Chiraphos, R = Ph, R‘ = Is = 2,4,6-( i -Pr) 3 C 6 H 2 ), 5; R = Me, R‘ = Mes*, 6; diphos* = R-Tol-Binap, R = Me, R‘ = Mes*, 7 ) containing chiral diphosphine ligands has been prepared by deprotonation of the cations [Pt(diphos*)(Me)(PHRR‘)][BF 4 ] 2, 3, and 4, respectively. The cations, synthesized from Pt(diphos*)(Me)(Cl), AgBF 4, and the appropriate secondary phosphine, were isolated as a mixture of diastereomers ( 2 and 3 ) or a single isomer ( 4 ). Phosphido complexes 1 and 5 − 7 show only one set of 31 P NMR resonances in solution even at low temperature, consistent either with the existence of a single diastereomer or with rapid inversion at phosphorus. However, low-temperature spectra of 13 and 14 reveal the existence of the expected two diastereomers, which interconvert by phosphorus inversion and rotation about the Pt−P bond with barriers of approximately 11.5 and 15.5 kcal/mol, respectively. Treatment of 6 and 7 with HBF 4 protonates the phosphido ligand and generates diastereomeric mixtures of the cations 3 and 4, respectively. Acrylonitrile inserts into the Pt−P bond of 1 to give the dialkyl complex Pt(dppe)(Me)[CH(CN)CH 2 P(Mes)(Men)] ( 9 ) as a mixture of four diastereomers; similar product mixtures ( 10 − 12 ) are obtained with 5 − 7 . Complexes 4 ·3CH 2 Cl 2, 5, and the secondary phosphine PH(Me)(Mes*) ( 8 ) were structurally characterized by X-ray crystallography.